1. Field of the Invention
This invention concerns an apparatus for measuring the polarization state of an incident light beam of a given width, the polarization properties of lenses, and the birefringence of optical elements.
2. Description of the Prior Art
In the prior art, devices that can measure polarization have been used to measure the polarization properties of elements, such as optical parallel plates. In conventional devices, a polarizer and an analyzer are disposed between an optical source that emits a light beam of a diameter of approximately 1 mm, and a photodetector, the element to be measured being interposed between these polarizing plates, and the amount of light transmitted being detected while the analyzer is rotated.
It is then possible to calculate at least the inclination of the polarization ellipse from the amount of light detected and the rotation angle of the analyzer.
These conventional devices, however, perform measurements on a narrow light beam. To obtain information in two dimensions, a mechanism was necessary to scan the specimen, which necessarily made the device more complex. And the measurement itself took a considerable time to perform.
Further, conventional devices were able to measure the polarization properties only of reflecting surfaces and flat plates, and could not be used to measure the polarization of lenses.
Conventional devices to measure the property of birefringence, on the other hand, are disclosed in Japanese Patent Early Laid-open Publication No. Sho 63-269045.
In the devices described in this Publication, the specimen is placed between a polarizer and an analyzer arranged in an orthogonal Nicol fashion, and the transmitted beam is received by a video camera while the orthogonal Nicol is rotated. In this measurement, the maximum light intensity and the rotation angle which gives this maximum intensity are found, and the birefringence of the specimen is calculated as a function of the rotation angle of the Nicol.
To measure birefringence with the above device, however, the light intensity must be measured with respect to a rotation angle of the Nicol at a large number of points. The measurement therefore requires a considerable amount of time, and the large amount of data obtained also requires a considerable amount of time to process.